This invention relates to an apparatus for freeze-drying products contained in receptacles such as bottles, vials, and the like. The apparatus is of the type which has a chamber, a plurality of vertically shiftable shelf plates and at least one plate shifting rod by means of which the shelf plates are moved. The plate shifting rod-actuating device is arranged externally of the chamber.
Freeze-drying processes are utilized mainly for preserving temperature sensitive products in order to retain their properties unchanged. The principal fields where freeze-drying is practiced are pharmacy, biology and medicine.
The conventional freeze-drying process has generally the following steps: during a first phase the water-containing product is frozen, for example, at a shelf plate temperature of -40.degree. C. Thereafter, a sublimation of the water--present in ice form--is effected under vacuum, approximately at a pressure of 10.sup.-1 mbar. After such a principal drying a postdrying is performed to achieve an extremely low residual water content. During the post-drying the product is warmed to the extent possible. The pressure at which the postdrying takes place is at approximately 10.sup.-3 mbar.
Apparatus for performing freeze-drying of the above-outlined type are known and are described, for example, in U.S. Pat. Nos. 3,448,556 and 3,451,189. These prior art arrangements relate to large freeze-drying installations where the product (such as vaccination substances, enzymes, vitamins, hormones, viruses, and the like) to be lyophilized is in a plurality of small containers. For performing the freeze-drying process, the containers are positioned on height-variable shelf plates. Each container is provided on its top with a special closure plug which, during the course of the freeze-drying process presents only a slight resistance to the outflow of water vapors. Upon conclusion of the freeze-drying process, the shelf plates are pushed together with the aid of a plate shifting rod which is introduced into the chamber. In this manner, the plugs are pressed into the openings of the respective containers for sealing the same. The chamber is opened and the freeze-dried products are removed only after the containers are hermetically closed as described.
During the above-described freeze-drying process particularly stringent requirements are set for environmental sterility. For this reason it is conventional to sterilize the entire installation (the freeze-drying chamber, the condenser and other components) either before introducing every new charge of product to be lyophilized or at desired intervals. For this purpose, for example, saturated vapor with a predetermined pressure is introduced into the previously evacuated installation. The sterilizing temperature is conventionally approximately 125.degree. C. which corresponds to a pressure of approximately 2.3 bar. After a period of approximately 25 minutes the vapor is released, while a slight residual pressure is maintained in the chamber. Thereafter, the chamber and the condenser are dried by evacuation with a liquid seal pump at a pressure of approximately 50 mbar, and the shelf plate system is re-cooled to the charging temperature.
The freeze-drying chamber is charged with the receptacles which contain the product to be lyophilized only after the above-described sterilizing process has been performed. The containers themselves have been previously subjected to a sterilizing process. Furthermore, the charging process itself is performed from a sterile space.
If, in the freeze-drying processes described in the above-identified United States patents, during the charging process or at he end of the freeze-drying process the plate shifting rod is introduced into the chamber in order to alter the height of the shelf plates or to push the containers towards one another, a non-sterile portion of the plate shifting rod gains access to the chamber which, upon conclusion of the freeze-drying process, may still be under a pressure of approximately 10.sup.-3 mbar. During such a period the risks are high that an undesired contamination of the product occurs.